The present invention relates to fluorine-containing vinyl ethers, their polymers and copolymers, and resist compositions using such polymers and copolymers.
Hitherto, fluorine-containing polymers have been used in various fields, since they are superior in heat resistance and chemical resistance. In particular, amorphous fluorine-containing polymers are further superior in transparency, and therefore they have been used and studied in the fields of optical fiber and resist composition (see Japanese Patent Application Publication 2002-201231). In fact, the introduction of fluorine atoms lowers refractive index or improves transparency of the vacuum ultraviolet region light.
In the development of resist compositions (see Y. Kamon et al., J. Photopolym. Sci. Technol., 15, 535 (2002)), now, a major resist type is a positive-type resist composition, in which an acid is generated by light irradiation and then solubility of a resin of the resist composition in alkali aqueous solution changes due to a chemical change of the resin by an action of the acid as a catalyst. In the trend toward shorter wavelength light source to manufacture smaller semiconductor devices, there are problems that resins (e.g., novolak resins and acrylic resins) used in current resists are insufficient in transparency. Thus, there are a demand for polymers that contain fluorine atoms, do not contain structures such as carbonyl, and are superior in heat resistance and solubility in various solvents, and a demand for monomers for synthesizing such polymers.
Recent research and development have revealed that acrylic resins have a possibility to have relatively good resist characteristics (see Y. Kamon et al., J. Photopolym. Sci. Technol., 15, 535 (2002)). Acrylic resins, however, contain carbonyl structures that absorb vacuum ultraviolet light. Therefore, they are still not sufficient in transparency and are required to achieve further improvement.
Since conventional fluorine-containing monomers are inferior in copolymerizability with acrylic or methacrylic esters, it has been difficult to copolymerize acrylic monomers with fluorine-containing monomers. Thus, there are a demand for fluorine-containing monomers that do not have carbonyl structures and are superior in copolymerizability with acrylic or methacrylic monomers and a demand for copolymers of such fluorine-containing monomers and acrylic or methacrylic monomers.